Rainbow trout were subjected to 1 and 3h of environmental hypoxia (20Torr, 4°C), after which samples of blood, heart, brain, liver, and red and white muscle were removed for metabolite determination. The heart, brain and white muscle all showed signs of glycolytic activation. High-energy phosphate stores in the liver were greatly depleted, although there was no measurable decline in liver glycogen content. Glycolytic activation in the white muscle is argued to have a major impact on the hypoxia tolerance of trout, as this tissue produces the bulk of the lactate. These responses of the trout are contrasted with those of the African lungfish, a fish which is relatively tolerant of hypoxia.

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